This invention relates to a powder filling machine, by means of which a succession of containers receive a quantity of powder from a bulk supply thereof.
A known powder filling machine is shown diagrammatically in FIGS. 1 and 2 of the accompanying drawings, FIG. 1 being a side elevation and FIG. 2 being a vertical section showing the machine in a direction at right angles to FIG. 1.
The machine shown in FIGS. 1 and 2 comprises a filling wheel 2 rotatable about a horizontal axis by means of a horizontal shaft 4. The circumference of the filling wheel 2 has a plurality of radially extending ports 6, of which only two are shown in FIG. 2. Each port 6 has a piston 8 which, with the wall of the port 6, defines a chamber 10. The size of the chambers 10 can be altered by sliding the pistons 8 inwardly or outwardly in the ports 6. A hopper 12 is positioned immediately above the filling wheel 2 and contains a supply of powder. Below the filling wheel 2 is a conveyor mechanism, represented diagrammatically by line 14, which presents a succession of containers 16, of which one is illustrated, immediately beneath the filling wheel.
In use, a supply of powder is placed in the hopper 12 and is stirred throughout the process described below to maintain a homogeneous mix. The filling wheel 2 is rotated by the shaft 4 with an indexing motion. As each chamber 10 is positioned below the hopper 12 a predetermined volume of powder is drawn into the chamber to form a plug of powder therein, by the application of vacuum to the chamber. The means for applying vacuum are not shown. The amount of powder drawn in depends on the volume of the chamber which, in turn, depends on the position of the piston 8. The powder continues to be held in the chamber under vacuum until it reaches a position where it is vertically above the container 16 to be filled. At this point air, nitrogen or carbon dioxide, for example, at a little above atmospheric pressure is applied to the chamber to expel the powder into the container. The emptied chamber then continues its indexing motion back to the hopper. One modification of the system just described is to hold each container 16 in position below the filling wheel for long enough to receive a plurality of plugs of powder by discharge from a corresponding plurality of chambers. This makes it possible to use the same machine for filling containers with a wider range of fill weights or volumes. One use for the powder filling machine just described is in introducing pharmaceutical materials, for example ranitidine, into containers. The volume of such containers is typically from 8 ml to 127 ml, and the weight of powder to be introduced is in the range of from 1/4 to 10 g or more, for example 350 or 450 mg, ideally in one shot.
The known machine just described uses, as has just been mentioned, a filling wheel which rotates with an indexing motion. This gives rise to a number of disadvantages. One of these is that the speed at which the wheel can rotate is necessarily much less than the speed at which it could rotate were it doing so continuously. As a consequence, the number of containers which can be filled per unit time is considerably less than the number which could be filled were the machine not rotating with an indexing motion. Also, the indexing motion requires a sophisticated timing mechanism to ensure that a container is correctly positioned with respect to a chamber at the moment when powder is being discharged from the chamber. The necessity for such a timing mechanism gives rise to the possibility of error, and in any case increases the cost of the machine.
Examples of such known filling machines are disclosed in U.S. Pat. No. 4,640,448 (TL Systems Corporation), German Published application No. 31 20 017 (Zanasi Nigris S.p.A.) and U.S. Pat. No. 4,671,430 (Eli Lilly and Company).
British Patent No. 2094267 B (IMA-Industria Macchine Automatiche SpA) describes a machine for feeding predetermined quantities of tea and the like onto a web of filter material to form tea bags. The tea is fed from a generally horizontal filling wheel having recesses which are filled with the tea by means of plungers.
U.S. Pat. No. 2,907,357 (American Cyanamid Company) discloses a powder filling machine for bottles wherein a powder measuring roll rotates about a horizontal axis and feeds powder to a funnel plate rotating about a vertical axis. The funnel plate comprises a plurality of funnels arranged above a plurality of bottles which are carried about an axis colinear with the funnel plate axis.